Finely chop the onion. Next, melt butter in a pan and sauté the onion until translucent in about 3 minutes. Add the mustard. Stir in the flour and let it simmer gently for about 1 minute, stirring occasionally. While stirring, add 1/3 of the stock and continue stirring until the mixture is smoothly thickened. Stir in the rest of the stock, a little at a time.

Now let the soup simmer gently for about 5 minutes, stirring occasionally. Add the cream and the Boer'n Trots Koe cheese and let the cheese melt gently while stirring. Season the soup to taste with salt and pepper and, if desired, sprinkle the finely chopped greens of the spring onions over it. Serve with a thick slice of farmhouse bread.